Background: Benign lichenoid keratosis (BLK) is a well-known clinicopathologic entity and several histopathologic patterns have been described. Features mimicking mycosis fungoides (MF) in clinically typical BLKs have not yet been emphasized. The aim of this study was to confirm the occurrence of an MF-like pattern of BLK. Methods: A retrospective survey was conducted on cases diagnosed as BLK over a 9-month period in a regional dermatopathology service. Seven histologic parameters, previously confirmed as diagnostically suggestive of MF, were applied. Inclusion criteria were: three or more MF-related histologic features and a size less than 2 cm. The clinical features were reviewed. Results: Fifteen cases of MF-pattern BLK were identified. The number of MF-like parameters present in individual cases exceeded the inclusion criteria by variable amounts. Pautrier microabscesses and alignment of lymphocytes along the basal layer were the most frequent (14/15). The age of the patients ranged from 28 to 83 years, with a mean of 50. The size of the lesions ranged from 0.2 to 1.8cm, with a mean of 0.6cm. The upper trunk was the favored site. Most of the lesions had been removed because of suspicion of cutaneous malignancy; basal cell carcinoma was the most frequent clinical diagnosis. Conclusion: We describe an MF-like histologic pattern of BLK. Pathologists and dermatopathologists should be aware of this novel histologic pattern to facilitate distinction between the two disorders.

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Department of Dermatology, King Khalid University Hospital and Faculty of Medicine at King Saud University